The present invention is directed to a control system for linear actuator devices, and more particularly to a control system for linear actuator devices utilized upon a floor maintenance machine.
For purposes of convenience, the invention will be described in conjunction with a presently preferred implementation thereof embodied in an electric linear actuator. It will be understood, however, that the principles of the invention may apply equally as well to devices of analogous structure.
The design of automatic floor cleaning equipment often involves a considerable amount of rotary and/or linear motion actuation and control. Positioning of structures such as cleaning heads and squeegees must be accomplished quickly and transparently to the operator. The traditional method of controlling motion on cleaning equipment utilizes limit switches or other proximity switches that either directly control the power to one or more linear actuators, e.g., via relay switches, etc., or indirectly control linear actuators via a signal sent to a CPU indicating the position of the actuators. These switches introduce negative reliability and assembly issues into the design of the machine. For example, an actuator or linkage could be damaged if a jam occurs in mid stroke of the actuator as current would continue to be supplied to the actuator. Additionally, limit switches may become contaminated or damaged through the operation of the machine. The switches may also be misaligned during the assembly of the machine. Any of these situations can cause the actuator to stall, overheat, and/or damage the linkage or associated structure coupled thereto.
In mobile equipment systems that include a plurality of electric and or hydraulic devices, such as servo actuators, motors and pumps, it is conventional practice to couple all of such devices to a remote master controller for coordinating or orchestrating device operation to perform a desired task. Motors and actuators may be employed, for example, at several coordinated stages of a surface cleaning machine for automated control of fluids and surface working devices. In accordance with conventional practice, the master controller may comprise a programmable controller or the like coupled to the various remotely-positioned devices. Feedback from the remote devices may be provided via control signals therefrom. For closed-loop operation, a sensor may be coupled to each device for sensing operation thereof, and feeding a corresponding signal to the master controller through an analog-to-digital converter, etc.
Thus, in a system that embodies a plurality of electric and/or hydraulic devices, a substantial quantity of electrical conductors must be provided for feeding individual control signals to the various devices and returning sensor signals to the master controller. Such conductors interfere with system design and operation, and are subject to failure. The bank of D/A and A/D converters for feeding signals to and from the master controller add to the expense and complexity of the overall system. Perhaps most importantly, system performance is limited by capabilities of the master controller. For example, a programmable controller may require one hundred milliseconds to scan a device sensor signal, compute a new control signal and transmit such control signal to the remote device. An overburdened programmable controller may not perform acceptably in high performance applications that may require a ten millisecond response time, for example, at each of a plurality of remote devices.
The present invention relates to a linear actuator control system exhibiting improved performance. To solve some of these limitations associated with the prior art devices, a control system has been implemented in which the speed and force from the actuator can be independently controlled from a control processing unit (CPU). In a system according to the present invention, the CPU can monitor the force being delivered to the actuator and that information can be used to deduce the force and/or position of the actuator. This information can also be used to determine that the actuator has reached the end of its stroke. A system according to the present invention has the ability to reduce or terminate the power being delivered to the load device in order to prevent damage to the device. The reaction time of this protection circuitry is short enough to prevent damage to the load and the energy control circuitry. Importantly, such a system can eliminate the position sensing devices normally used in this type of machine.
The present invention relates to a control system for one or more linear actuator devices, such as present on a surface maintenance machine. One aspect of the invention is to provide a linear actuator control system for use on a surface maintenance machine, such as a scrubber or sweeper, which utilizes a comparison circuit in which a signal representative of the load current in an linear actuator is modified by a signal representative of the desired load current to maintain applied load current at a desired level.
Another aspect of the present invention provides a control system which automatically limits the current load to a linear actuator in the event of an abnormal condition, e.g. linkage jamming, obstruction contact, etc.
Another aspect of the present invention provides a control system for automatically controlling one or more linear actuators of a surface maintenance machine which may be applied to various types of surface maintenance machines having different surface maintenance tools and providing for different surface maintenance functions.
A linear actuator control system in accordance with a further aspect of the invention includes a linear actuator having an electric motor component. The electric motor component is connected to drive circuitry that includes a solid state switch, preferably a FET, that is connected between one terminal of the electric motor, with the other terminal being connected to electrical ground. The control switch circuit receives a switch control signal from the microprocessor-based control electronics, and is connected to the control electrode (gate) of the FET for setting the switch circuit and controlling power to the electric motor of the linear actuator through the FET in response to the control signal. Feedback circuitry is responsive to the current through the electric motor for resetting the switch circuit and interrupting application of power to the electric motor. The feedback circuitry is responsive to a voltage drop across a shunt resistor.
It is therefore a general object of the present invention to provide a linear actuator control system that exhibits a fast response time necessary for high performance applications, while at the same time reducing cost and complexity that are inherent in prior art system of the character described above. In furtherance of the foregoing, a more specific object of the invention is to provide a system of the described character wherein each of the system linear actuators embodies microprocessor-based control adapted to communicate with a central or master controller and for thereby distributing, at least partial, control of the several linear actuators while maintaining overall coordination thereamong.
Another object of the present invention is to provide a linear actuator control structure in which all control components, including current level detectors and microprocessor-based control electronics, are fully integrated into compact inexpensive packages, and which may be readily employed in a wide variety of system applications.
Yet another object of the invention is to provide a linear actuator of the described character with enhanced robustness of hardware, including the elimination of limit switches or other position detection devices within or in association with the linear actuator.
Still another object of the present invention is to provide a system for controlling a linear actuator device, with control electronics that limit current overload as compared with prior art devices of a similar character, and that have enhanced capabilities for protecting the linear actuator against damage due to structure obstruction, contact, etc.